January 31, 2013

Extreme Space Weather Triggered Medieval Famines, Say Astrophysicists

Famines plagued Iceland and food prices spiked in medieval England following extreme space weather events, according to a new study of historical data

The Earth’s local interplanetary environment is a maelstrom of solar winds, giant clouds of hot plasma ejected from the Sun and violent magnetic fields. To a large extent, we are protected from this so-called space weather by our atmosphere and the Earth’s magnetic field.

But every once in a while, these interplanetary storms are so ferocious that even our planetary defences fail. In 1989, for example, a powerful geomagnetic storm knocked out the Hydro-Quebec power grid leaving six million people without electricity.

Today, Lev Pustil’nikand Gregory Yom Din at Tel Aviv University in Israel say the effects of space weather could be much more significant than originally thought. These guys make the case that under certain special conditions, space weather can influence terrestrial weather so severely that it can have a dramatic effects on agriculture, causing crop failures, death and starvation.

The evidence linking space weather and terrestrial weather is growing. The idea here is that cosmic rays can ionise dust particles, which then attract water vapour triggering the formation of clouds.

This happens only in regions where the atmosphere is in a critical state with high enough levels of humidity. For example, there is growing evidence that this seems to have happened many times in the cold moist air over the North Atlantic.

This alone cannot influence agricultural output under ordinary conditions, however. Pustil’nik and Yom Din point out that certain crops are hugely vulnerable to dramatic changes in weather at specific times of the year. For example, a cold snap lasting a few days can destroy certain crops without influencing the annual or even monthly mean temperature. If a region is overly dependent on these kinds of crops, then it is vulnerable to the cascading effects of space weather.

But even this need not lead to catastrophe if the local population can easily access food from elsewhere. So one final factor also comes into play which is a region’s isolation.

So their theory is that a region’s agriculture is vulnerable to variations in space weather if it meets three conditions: the local weather must be sensitive to space weather; the local agriculture must be critically vulnerable to sudden changes in weather; and finally, the region must be isolated.

Pustil’nik and Yom Din say that several regions meet these criteria and predict that there ought to be a correlation between space weather and the price of food in these places.

One place they pick out is medieval England, which is vulnerable because it is in the north Atlantic, dependent on wheat which is vulnerable to weather changes and also isolated from mainland Europe.

So an interesting question is whether food prices in medieval England correlate with space weather records.

That sounds a tall order to investigate given the nature of the data. But as it turns out, detailed records of English food prices survive dating back to 1259.

What’s more, accurate space weather records as measured by the number of sunspots date back to the time of Galileo and can be extrapolated further back using other dating methods.

That’s allowed Pustil’nik and Yom Din to look for correlations between the two. Sure enough, they say that wheat prices are significantly correlated with space weather events such as solar maxima and minima, particularly during the so-called Maunder minimum between 1580 and 1700 when solar activity was low.

“All the nine cycles of solar activity during this period are characterized by systematically excessive wheat prices in the years of solar activity minimum, as compared with the prices during the next maximum,” they say, adding that the level of significance is in excess of 99%.

These guys have combed ancient records for a number of other vulnerable places such as Iceland and parts of medieval Europa and say that similar correlations exist there as well. In particular, they say that space weather and famines are strongly correlated in Iceland between 1770 and 1900.

That’s an interesting result that has important implications for the future. It’s easy to imagine that Earth is less vulnerable now to this kind of problem because the global food market means that few places are genuinely isolated from the rest of the world.

However, Pustil’nik and Yom Din say that global warming is pushing more regions closer to the type of critical vulnerability that makes space weather a worry.

That’s something that agriculturists, climatologists and space weather experts might want to investigate together in more detail.